Thursday's clashes, in which several people were wounded, erupted when a few hundred Tuareg protesters prevented the prime minister's plane from landing in Kidal.

The central government said soldiers at the airport had been "taken to task by uncontrollable elements" and had fired warning shots after being shot at and hit with stones. But the MNLA said the soldiers had fired directly at a crowd that included women and children.

"What happened is a declaration of war. We will deliver this war," the MNLA's vice-president, Mahamadou Djeri Maiga, told the AFP news agency. "Wherever we find the Malian army we will launch the assault against them. It will be automatic. The warnings are over."

Reuters also quoted a statement by one of the MNLA's founders, Attaye Ag Mohamed, as saying the "political and military wings of the Azawad" had declared "the lifting of the ceasefire with the central government".

The MNLA launched an insurgency to take control of northern Mali and establish an independent homeland they call Azawad in January 2012.

A subsequent coup in Bamako led to chaos that was exploited by Islamist militants linked to al-Qaeda who took control of the north.

The militants were eventually ousted by a French-led military operation launched in January 2013.

The June ceasefire agreement led to residents of Kidal, an MNLA stronghold, being allowed to vote in both rounds of the presidential election in July and August.